低温条件下无定型硅铝的硅铝比对Ni2P催化剂制备的影响

采用分步沉淀法制备了SiO₂和不同质量硅铝比(包括9/1,8/2,7/3和6/4)的无定型SiO₂-Al₂O₃(ASA),采用饱和体积共浸渍和程序升温还原法制备Ni₂P/ASA催化剂,以X射线衍射(XRD)、普通红外(FT-IR),N₂吸附脱附、H₂还原脱附(H₂-TPR)和透射电镜(TEM)对载体和催化剂进行表征,重点考察了低温条件下不同硅铝比以及比表面积大小对Ni₂P相生成的影响。结果表明,在低温条件下,载体中氧化铝含量增多,生成Ni₂P相所需的P含量越多。原因是磷首先与氧化铝生成AlPO₄相,阻碍了富磷气氛的生成,而生成Ni₂P相必须在富P的气氛下进行,从而在铝含量较多的载体中必须加入更多的P含量才能生成纯Ni₂P相。而TEM结果则表明,AlPO₄相的生成反过来促进了Ni₂P颗粒尺寸的降低,有利于催化剂的分散。载体比表面积大小对Ni₂P相的生成影响不大。

Effect of Si/Al ratio of Amorphous SiO2-Al2O3 on Preparation of Ni2P catalyst under low temperature condition

The SiO₂ and amorphous SiO₂-Al₂O₃ (ASA) was prepared by stepwise precipitation method, and the Ni₂P/ASA catalyst was fabricated by saturated volume impregnation and programmed-temperature reduction. Characterizations of the supports and catalysts were performed using XRD, FT-IR, N₂ adsorption-desorption, H₂-TPR and TEM, and then the effects of mass SiO₂/Al₂O₃ ratio and specific surface area obtained with ASA on the Ni₂P formation were mainly investigated. Results showed that with the increasing of Al₂O₃ content in ASA support the more content of P was required for the formation of Ni₂P phase. Reason was that phosphorus firstly formed AlPO₄ phase with alumina, hindered the formation of phosphorus-rich atmosphere, however phosphorus-rich atmosphere was pre-requisited to the formation of Ni₂P phase, hence more P must be added to the carrier with more aluminum content to produce pure Ni₂P phase. And TEM results indicated that the formation of AlPO₄ phase, in turn, promoted the reduction of Ni₂P particle size and facilitated the dispersion of the catalyst. The specific surface area of the support has little influence on the formation of Ni₂P phase